Fabricated centrifugal impeller assembly

ABSTRACT

A fabricated centrifugal impeller assembly is provided which resists failure due to cyclic stressing. The impeller assembly includes a hub, and a plurality of blades. Each blade has a tab adjacent its axis of rotation, with the tab extending generally perpendicularly to the radially extending main portion of the blade. A blade retainer is positioned with its back surface adjacent the hub to clamp the tabs between the blade retainer and the hub. The blade retainer includes a plurality of slots that permit insertion of a blade therethrough with the tab of each blade extending in generally abutting contact with the back surface of the blade retainer. Compression means connect the blade retainer and the hub and exert a compressive force that clamps the blade retainer and the tabs against the hub. The tabs and blade retainer permit attaching separate fabricated blades to the hub of an impeller assembly in a manner which does not disrupt the flow contours of the impeller inlet area.

United States Patent FOREIGN PATENTS 482,965 7/1953 ltaly 580,119 8/1946 GreatBritain ABSTRACT: A fabricated centrifugal impeller assembly is provided which resists failure due to cyclic stressing. The impeller assembly includes a hub, and a plurality of blades. Each blade has a tab adjacent its axis of rotation, with the tab extending generally perpendicularly to the radially extending main portion of the blade. A blade retainer is positioned with its back surface adjacent the hub to clamp the tabs between the blade retainer and the hub. The blade retainer includes a plurality of slots that permit insertion of a blade therethrough with the tab of each blade extending in generally abutting contact with the back surface of the blade retainer. Compression means connect the blade retainer and the hub and exert a compressive force that clamps the blade retainer and the tabs against the hub. The tabs and blade retainer permit attaching separate fabricated blades to the hub of an impeller assembly in a manner which does not disrupt the flow contours of the impeller inlet area.

Patented March 30, 1971 3 Sheets-Sheet 1 INVENTORS ROBERT E. SCHRETER JOHN A.|MARINO JOHN OHARA flllegarz, jfe/zawsolz @JaZaow ATTORNEYS Patented March 30, 1971 3,572,967

3 Sheets-Sheet 2 mvm'rons ROBERT E. SCHRETER JOHN AMARINO JOHN OHARA E r magma J e/zc/mo/z @zja oa/ ATTOR N EYS Patented March 30, 1971 3,572,967

5 Sheets-Sheet S 7 INVENTORS ROBERT E. SCHRETER JOHN AMARINO JOHN O HARA Elwyn/2, l elza'wsm QzTzafiow ATTORNEYS FABRICATTLB CENTRIFUGAL IMPELLER ASSEMBLY adjacent the axis of the casing and a discharge opening at the outer opening adjacent the axis of the casing and a discharge opening at the outer radius of the casing. A a gas, such as air, is drawn into the impeller which imparts a high velocity to the air. The high velocity air emerges from the impeller, where its kinetic energy can be utilized.

' The inlet of a centrifugal blower receives a basically axial flow of air and converts this axial flow of air to a radial flow. It is thus desirable the that the inlet end of the centrifugal impeller assembly possess a smooth, unobstructed contour to minimize the frictional losses which occur during this change of flow direction.

To provide structural rigidity to withstand the dynamic loading of the impeller assembly, the inlet edge of the blade, which is fastened to a peripheral shroud, must also be attached to a central hub. The area where the blade is supported at the hub is a high stress area which is subject to cyclic loadings caused by vibration of the leading edge of the blade and caused by shroud rotational vibration. This cyclic stressing and the force required to keep the centrifugal load on the blades from bending a backplate which is attached to the backside of the blades, must be absorbed at the pointof attachment of the leading leading edge of the blade to the hub.

In the past, the inlet edge of the blade has usually been attached to the, hub of a fabricated centrifugal impeller assembly by either welding the leading edge of the blade to the hub or by riveting the blade directly to the hub section. Most of the prior art designs for connecting the leading edge'of the blade and the hub have not provided the proper contours to efficiently turn the axial inlet flow to a radial direction, and have consequently resulted in excessive frictional losses.

While welding has been used to fabricate some centrifugal impeller assemblies which possess a desirable flow path, it is often undesirable to weld in areas known to be subject to high cyclic stress loading, unless the assembly is fabricated of easily welded materials and is stress relieved, because of the probability of failure at the weld area. If welding is used to structurally connect the blades and the hub, the available materials of construction for the blade and the hub are drastically narrowed; that is, only materials which are compatible for welding purposes can be used.

In accordance with the present invention, the blades are manufactured with a short tab on their inlet edge, with the tab being bent to provide a surface generally out from the substantially radially extending blade. The compressive force needed to clamp the blade to the hub is provided by a blade retainer which applies a compressive load against each of these tabs, thus clamping them to the main hub body. The compressive force is applied through the outer diameter of the blade retainer and through the blade tabs and is transferred to the portion of the hub directly beneath the tabs. The compressive force is applied to the blade retainer bya compression means, such as a stud and locknut which connects the blade retainer and hub.

The invention consists in the novel parts, constructions, arrangements, combinations and improvements shown and described. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention, and, together with the description, serve to explain the principles of the invention.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention.

in the drawings:

FIG. I is a side elevation view partly in section of a fabricated centrifugal impeller assembly constructed in accordance with the invention;

FIG. 2 is an end elevation view of the assembly of FIG. ll;

FIG. 3 is an end elevation view of the blade retainer illustrated in FIG. 1;

FIG. 4 is a section view of the blade retainer taken along line 4-4 of FIG. 3',

FIG. 5 is an enlarged end view of one of the blades as it appears in FIG. 2;

FIG. 6 is a side view of a blade; and

FIG. 7 is an end view of a blade looking from the tip inwardly along the radius of the blade.

A centrifugal impeller which is particularly well suited for use in a combustion blower is illustrated in the drawings. In use as a combustion blower, the impeller assembly is mounted on a driven rotating shaft and enclosed in a disc-shaped casing which possesses an axial inlet opening and a peripheral discharge opening.

In accordance with, the invention, a hub is provided which can be mounted for rotation on a rotatable shaft. Preferably, the hub is symmetrical about a central axis and tapers smoothly rearwardly from a first radius adjacent the inlet opening of the blower casing to a second larger radius. Thus, the hub assists in changing the generally axial inlet flow of air to a radial flow, as shown by flow direction arrows I0 illustrated in FIG. ll.

As here embodied, a hub generally 12 is provided which is substantially symmetrical about a central axis I4. Hub I2 includes a blade-seating portion 16, and a rearwardly positioned shaft seating portion 18 which includes a central opening 20 for insertion of a driven shaft (not shown) which drives the impeller assembly. Blade-seating portion It includes a tabmounting surface 22 at its forward (inlet) end and a backplate-mounting surface 24 at its rear. These surfaces extend generally perpendicular to axis 14. When viewed along axis I4, blade-seating portion 16 has a circular cross section and tapers smoothly from the tab-mounting surface to the larger diameter backplate mounting-surface, and thus helps minimize frictional losses as the fluid flow is changed from an axial to a radial direction through contact with the hub.

As illustrated in FIGS. 11 and 2, the hub preferably has a plurality of threaded circular openings 26 for attachment of a backplate to the hub. Two setscrew openings 2% are provided in shaft seating portion l8 to rightly mount the hub on a rotatable shaft. A threaded central openingis provided at the forward (inlet) end of the hub for insertion of compression means, as described below. Desirably a bushing 30 is inserted in central opening 20 to provide a precise cylindrical wall surface for insertion of the rotating drive shaft.

In accordance with the invention, a plurality of radially extending blades are provided for forcing an incoming axial flow of fluid to a centrifugally outward direction at a velocity which exceeds the inlet velocity of flow of the fluid. The blades each have a tab on their inlet edge which extends out from the surface of the radially extending blades. The tabs provide a convenient, failure resistant means for attaching the leading edge of the blade to the hub without destroying the smooth contour of the inlet portion of the impeller assembly. The smooth contour is highly desirable to avoid excessive friction losses in the fluid stream.

As here embodied and as illustrated in FIGS. 1 and 2, a plu rality of blades 40 extend in a generally radial direction from hub 12 to the outer periphery of the impeller assembly. As best seen in FIGS. 5-7, a tab 42 extends from the inlet edge of each blade at the end of the blade adjacent axis 114. Preferably the tab is planar and generally rectangular, and extends in a generally perpendicular direction to the adjacent radially extending portion of the blade. As illustrated in FIG. I, tabs 42 are thus aligned in a plane generally transverse of axis l4 when the blades are mounted in the impeller assembly.

As here embodied and as illustrated in FIGS. 5-7, blades 40 include a shroud-mounting flange &6 and a bacltplatemounting flange ad which are attached, preferably by rivets 543 as illustrated in HO. 1, to a shroud 52 and a backplate 54, respectively. The shroud, the outer portion of the blades, and the backplate thus cooperate to form a plurality of radially extending fluid flow passages which extend to the periphery of the impeller assembly. The cross section of these passages is preferably contoured to provide a constant average velocity from the inlet end to the discharge end of the impeller assembly.

In accordance with the invention, a blade retainer is positioned with its back surface adjacent the hub to clamp the tabs of the blades between the blade retainer and the hub. The blade retainer includes a plurality of slots extending inwardly in a generally radial direction from the perimeter of the blade retainer to permit insertion of a blade through a slot with its tab extending in generally abutting contact with the back surface of the blade retainer to permit insertion of a blade through a slot with its tab extending in generally abutting contact with the back surface of the blade retainer. Preferably, the blade retainer is symmetrical about a central axis and tapers rearwardly from a small radius at its front to a large radius which is approximately equal to the front radius of the hub. Thus, the blade retainer and the hub present a smoothly tapering surface which cooperates with the inlet portion of the blade to smoothly change the direction of fluid flow from an axial inlet direction to a radial discharge direction with a minimum of turbulence.

As here embodied, and as illustrated in FIGS. 3 and 4, a blade retainer generally 60 is provided which has the general shape of a truncated cone. The sloping wall surfaces of the blade retainer include a plurality of slots 62 extending inwardly in a generally radial direction from the perimeter of the back surface of the blade retainer. The width of slots 62 slightly exceeds the width of the leading edge of the blade and extends axially through the blade retainer to permit the insertion of the blade through the slots, and to permit the tab which extends from the blade to be positioned in generally abutting contact with the back surface of the blade retainer.

As best seen in FIG. 4, the back surface of blade retainer 60 includes a peripheral flange 63 for compressing the tabs against the hub and a central portion 70 which does not contact the hub when the tabs are compressed between the blade retainer and the hub. Thus, central portion 70 desirably does not protrude past flange 68, a distance which exceeds the thickness of tabs 42.

A longitudinally extending central opening 66 is provided for insertion of compression means, described below.

in accordance with the invention, compression means are provided which connect the blade retainer and the hub and exert a compressive force that clamps the blade retainer and the tabs of the blades against the hub. As here embodied, and as illustrated in FIG. i, the compression means comprise a threaded stud 76 and a locknut 78. The threaded stud and locknut permit the blades 41) and any attached shroud or backplate, to be removed from hub 12. Thus, it is possible to interchange various hub and blade designs to provide optimum flow conditions for various design capacities. For example, for optimum efficiency, the cross-sectional area of the impeller flow passages should provide for a constant average velocity gradient from the inlet to the exit of the impeller, at the impeller design flow. Therefore, the inlet area should be different for impeller assemblies with different design flows but using the same blades. A feature of the present invention is that the inlet area can be easily increased or decreased for different design flow capacities by merely changing the diameter of the blade retainer and the hub while still maintaining a standard-sized flange connection at the casing inlet.

Ordinarily, the impeller assembly of the present invention is assembled as shown in FIGS. 1 and 2 prior to being mounted on a driven shaft and prior to insertion into the casing of a centrifugal blower.

The sequence of assembling the elements of the impeller assembly is not critical. Thus, the following assembly procedure is merely illustrative of numerous assembly procedures which could be utilized.

The inner end of blades 40 are inserted through slots 62 of blade retainer 60 and the tabs 42 are aligned parallel with peripheral flange 63 of the blade retainer. Tabs 42 are seated on tab mounting surface 22 of hub 12 and then stud 76 is inserted through opening 27 in the hub and opening 66 in blade retainer 60. Subsequently, locknut 78 is screwed on the protruding end of the stud to clamp the blades and the blade retainer to the hub.

Subsequently, backplate 54 is connected to hub H2 by threaded bolts 80 which extend through opening 26 in the hub, backplate 54 is riveted to flange 48 of the blades, and shroud 52 is riveted to flange d6 of the blades.

The impeller assembly is nowready for insertion in a. blower casing, and for mounting on a power driven shaft.

The invention in its broader aspects is not limited to the specific details shown and described and departures may be made from such details without departing from the principles of the invention and without sacrificing its chief advantages.

We claim:

1. An efficient fabricated centrifugal impeller for'use in a centrifugal blower or compressor comprising:

a. a hub which is symmetrical about a central axis and is mounted for rotation on a rotatable shaft, said hub having an axially extending wall surface which tapers smoothly from a first radius adjacent the inlet rearwardly to a second larger radius;

b. a plurality of radially extending blades for forcing a flow of fluid in a centrifugally outward direction, each of said blades including at the end adjacent its axis of rotation, a

tab, said tab extending out from the radially extending main portion of the blade;

c. a blade retainer symmetrical about a central axis and having a wall surface which tapers smoothly from a small radius adjacent the inlet to a larger radius approximately equal to the first radius of said hub, said blade retainer including a plurality of slots extending inwardly from its perimeter and extending axially through said blade retainer, said blade retainer and said hub cooperating with said blades to form a smooth inlet surface for flow of air into the impeller assembly with minimum frictional loss; and

d. compression means connecting said blade retainer and said hub for exerting a compressive force that clamps said blade retainer and said tabs against said hub.

2. The impeller assembly of claim I in which said tabs extend in a generally perpendicular direction out from the main portion of the blade; and the blade retainer is generally symmetrical about a central axis, and has a back surface including a peripheral flange for compressing said tabs against said hub, said flange extending radially inwardly from the perimeter of said back surface; and a central portion which does not contact said hub when said tabs are compressed between said blade retainer and said hub.

3. The impeller assembly of claim I in which said blade retainer and said hub each include a central opening, and said compression means includes a stud extending through said central openings, and a locknut.

4. The impeller assembly of claim 1 including a generally planar annular shroud attached to the outer leading edge of the blade, and a generally planar backplate attached to the surface of said hub adjacent the rotating shaft, said backplate extending radially outwardly to the tip of said blades and attached to said blades, with said shroud and said backplate cooperating with said blades to form radially extending channels for directing the flow of fluid.

5. A fabricated centrifugal impeller assembly comprising:

a. a hub which can be mounted for rotation on a rotatable shaft;

b. a plurality of radially extending blades for forcing a flow of fluid in a centrifugaliy outward direction, each of said blades including at the end adjacent its axis of rotation, a tab, said tab extending out from the radially extending main portion of the blade;

c. a blade retainer positioned with its back surface adjacent said hub and including a plurality of slots extending inwardly in a generally radial direction from the perimeter of the blade retainer to permit insertion of a blade therethrough with its tab extending in generally abutting contact with the back surface of said blade retainer; and

d. compression means connecting said blade retainer and said hub for exerting a compressive force that clamps said blade retainer and said tabs against said hub.

6. The impeller assembly of claim 5 in which the blade retainer is generally symmetrical about a central axis, and has a back surface including a peripheral flange for compressing said tabs against said hub, said flange extending inwardly from the perimeter of said back surface; and a central portion which does not contact said hub when said tabs are compressed between said blade retainer and said hub.

7. The impeller assembly of claim 5 in which said blade retainer and said hub each include a central opening, and said compression means includes a stud extending through said central openings, and a locknut.

87 The impeller assembly of claim 5 including a generally planar annular shroud attached to the outer leading edge of the blade, and a generally planar backplate attached to the surface of said hub adjacent the rotating shaft, said backplate extending radially outwardly to the tip of said blades and attached to said blades, with said shroud and said backplate cooperating with said blades to form radially extending channels for directing the flow of fluid.

9. The impeller assembly of claim 8 in which said hub is connected to said backplate by a removable threaded means to permit interchangeable mounting of various blades and blade retainers on said hub.

10. The impeller assembly of claim 8 in which a plurality of individual flow passages are formed for the fluid by said blades, said blade retainer, said hub, said shroud, and said backplate with said flow passages terminating between said shroud and said backplate and the cross section of said flow passages contoured to provide a constant average velocity from the inlet end to the discharge end of the impeller assembly. 

1. An efficient fabricated centrifugal impeller for use in a centrifugal blower or compressor comprising: a. a hub which is symmetrical about a central axis and is mounted for rotation on a rotatable shaft, said hub having an axially extending wall surface which tapers smoothly from a first radius adjacent the inlet rearwardly to a second larger radius; b. a plurality of radially extending blades for forcing a flow of fluid in a centrifugally outward direction, each of said blades including at the end adJacent its axis of rotation, a tab, said tab extending out from the radially extending main portion of the blade; c. a blade retainer symmetrical about a central axis and having a wall surface which tapers smoothly from a small radius adjacent the inlet to a larger radius approximately equal to the first radius of said hub, said blade retainer including a plurality of slots extending inwardly from its perimeter and extending axially through said blade retainer, said blade retainer and said hub cooperating with said blades to form a smooth inlet surface for flow of air into the impeller assembly with minimum frictional loss; and d. compression means connecting said blade retainer and said hub for exerting a compressive force that clamps said blade retainer and said tabs against said hub.
 2. The impeller assembly of claim 1 in which said tabs extend in a generally perpendicular direction out from the main portion of the blade; and the blade retainer is generally symmetrical about a central axis, and has a back surface including a peripheral flange for compressing said tabs against said hub, said flange extending radially inwardly from the perimeter of said back surface; and a central portion which does not contact said hub when said tabs are compressed between said blade retainer and said hub.
 3. The impeller assembly of claim 1 in which said blade retainer and said hub each include a central opening, and said compression means includes a stud extending through said central openings, and a locknut.
 4. The impeller assembly of claim 1 including a generally planar annular shroud attached to the outer leading edge of the blade, and a generally planar backplate attached to the surface of said hub adjacent the rotating shaft, said backplate extending radially outwardly to the tip of said blades and attached to said blades, with said shroud and said backplate cooperating with said blades to form radially extending channels for directing the flow of fluid.
 5. A fabricated centrifugal impeller assembly comprising: a. a hub which can be mounted for rotation on a rotatable shaft; b. a plurality of radially extending blades for forcing a flow of fluid in a centrifugally outward direction, each of said blades including at the end adjacent its axis of rotation, a tab, said tab extending out from the radially extending main portion of the blade; c. a blade retainer positioned with its back surface adjacent said hub and including a plurality of slots extending inwardly in a generally radial direction from the perimeter of the blade retainer to permit insertion of a blade therethrough with its tab extending in generally abutting contact with the back surface of said blade retainer; and d. compression means connecting said blade retainer and said hub for exerting a compressive force that clamps said blade retainer and said tabs against said hub.
 6. The impeller assembly of claim 5 in which the blade retainer is generally symmetrical about a central axis, and has a back surface including a peripheral flange for compressing said tabs against said hub, said flange extending inwardly from the perimeter of said back surface; and a central portion which does not contact said hub when said tabs are compressed between said blade retainer and said hub.
 7. The impeller assembly of claim 5 in which said blade retainer and said hub each include a central opening, and said compression means includes a stud extending through said central openings, and a locknut.
 8. The impeller assembly of claim 5 including a generally planar annular shroud attached to the outer leading edge of the blade, and a generally planar backplate attached to the surface of said hub adjacent the rotating shaft, said backplate extending radially outwardly to the tip of said blades and attached to said blades, with said shroud and said backplate cooperating with said blades to form radially extending channels for directing the flow of fluid.
 9. The impeller assembly of claim 8 in whIch said hub is connected to said backplate by a removable threaded means to permit interchangeable mounting of various blades and blade retainers on said hub.
 10. The impeller assembly of claim 8 in which a plurality of individual flow passages are formed for the fluid by said blades, said blade retainer, said hub, said shroud, and said backplate with said flow passages terminating between said shroud and said backplate and the cross section of said flow passages contoured to provide a constant average velocity from the inlet end to the discharge end of the impeller assembly. 